Hello all,

Last year I changed the radiator when doing the 3vze rebuild. The old cap started to leak a bit of coolant through the top (see pic below) and I bought a new one, some english brand, seems to be almost the same, maybe a bit wider on the rubber gasket. Old cap wasn holding pressure all the time, sometimes it would "oouuffff" with vacuum when I open it, sometimes nothing. New cap keeps more vacuum every time and doesn leak through the top. However, after around 10-12 days of use I started seeing the coolant level on the radiator going low. Top metal inside wasnt swimming in coolant longer. I poured around 300-400 ml in, drove around 100 miles and checked it again - again "dry" to the same level. Filled again around 250 ml and put the old cap back on. After some 30 miles with it it leaks from the top again, but level is high, as expected (picture below). The overflow bottle stays the same level with both caps, it seems. Around the middle area, where it gets different shape.

No leaks on the ground.
What do you make of it? New cap bad or?

New cap

New cap

Old cap on a cool engine.

Side to side

Old cap

Old cap

Old cap

Coolant level with old cap.

 

I tried a third cap, while waiting for the OEM cap to arrive. A few days was holding the level, but today was dry. Added some destilled water (half liter). Noticed the overflow container was full almost to the top, as I left it after bleeding the system a few days ago. So the thing is - it keeps losing coolant in the radiator, but does not suck coolant from the overflow container when cooling down. Any thoughs on whats causing this?

 

Usually the overflow container only comes into play when the cooling system pressure exceeds the radiator caps pressure rating. In other words overheating, or excess pressure due to combustion pressure leaking into the cooling system (bad head gasket usually). If 3 caps have given you the same result I think it's time to look deeper into the system. Coolant doesn't just disappear, it's going somewhere.

 

does the cap on your overflow tank have the pickup tube attached that goes to the bottom of the tank?
as your cooling system heats up water/coolant flows to the tank when the pressure reaches the setpoint of the pressure cap, but when it cools down and pulls a vacuum it is supposed to also allow water/coolant to flow back to the radiator otherwise when you pop the cap it will be low on coolant.

 

Thanks for the replys, guys!

Moto809, dont know about that, but usually it flows to the overflow container only when I am bleeding the coolant system for air. Otherwise, the level in there does not rise.

Akwheeler, It does have a small tube that goes down, but not to the bottom of the tank, but just a couple of inches below the cap level. Its open at the end.

By the way, I got my OEM cap, driving around in it made the excess of coolant in the overflow tank be sucked back to the radiator in a matter of a few days. Now the level stays just above the "top" line indicator on the container.
The cap looks legit, but tends to keep twisting a a few degrees back when I check it at a total cool engine in the morning. Like, when fully shut, the "ears" stay in position 9 - 3 o'clock, right? And it twists back to around 7 - 1 o'clock. Is this normal? The cap twists to a full closing position with ease. Other than that, I havent seen it leaking, whatsoever.

 

But does it go down far enough to be submerged in the coolant? It will only draw fluid back into the radiator if it is IN the coolant and it needs to be.
Optimally it should be within an inch or less from the bottom of the overflow bottle but not touching.
Any air leaks in the line from the radiator to the overflow tank will stop it from maintaining a full radiator.
You could post a picture of your coolant bottle and the cap/pickup tube.
If you are convinced this is not your issue try pressure testing your cooling system and look for leaks.

 

Oh yes, it goes to the bottom. I thought you were talking about the pipe extention outside the overflow container.